This results in a simpler service unit which doesn't first have to
start a shell:
> cat /nix/store/s95nsr8zbkblklanqpkiap49mkwbaq45-unit-alertmanager.service/alertmanager.service
...
ExecStart=/nix/store/4g784lwcy7kp69hg0z2hfwkhjp2914lr-alertmanager-0.16.2-bin/bin/alertmanager \
--config.file /nix/store/p2c7fyi2jkkwq04z2flk84q4wyj2ggry-checked-config \
--web.listen-address [::1]:9093 \
--log.level warn
...
https://github.com/golang/go/issues/9334 describes how net.Listen (as used by Alertmanager):
* listens on 127.0.0.1 if the listenAddress is "localhost"
* listens on all interfaces if the listenAddress is ""
This commit adds an assertion that checks that either `configFile` or
`configuration` is configured for alertmanager. The alertmanager config
can not be an empty attributeset. The check executed with `amtool` fails
before the service even has the chance to start. We should probably not
allow a broken alertmanager configuration anyway.
This also introduces a test for alertmanager configuration that piggy
backs on the existing prometheus tests.
Alertmanager 0.13.0 doesn't support single dash long options, so '-config.file'
for example is parsed as '-c', which leads to the service not starting.
The reason being less mental overhead when reading upstream
documentation. Examples can be pasted right into the configuration
instead of translating to Nix attrset first.
The current default value of listenAddress = null blows up:
$ nixos-rebuild build
error: cannot coerce null to a string, at
.../nixpkgs/nixos/modules/services/monitoring/prometheus/alertmanager.nix:97:16
With listenAddress = "" we use the same default as upstream and there is
no blow up :-)
